In addition to T\(_{\rm {He}}\) , \(^{16}\) O/\(^{18}\) O can also depend on the extent of the convective envelope and the mass of hydrogen in the helium burning shell [1]}, [2]}. Munson et al. explored the effect of convective overshoot factor (f) on \(^{16}\) O/\(^{18}\) O. They found that for \(f<0.07\) , \(^{16}\) O/\(^{18}\) O \(\approx 1\) , but increases rapidly for \(f>0.07\) . Large values of f correspond to cases where the convective envelope extends all the way to the CO core and dredges up additional \(^{16}\) O from the core into the envelope. The high values of \(^{16}\) O/\(^{18}\) O in RCB stars could be partly explained due to such a deep convective dredge up. That will also reduce C/O in RCB stars compared to dLHdC stars. The initial conditions of a merging system that would give rise to a deep convective zone remain to be explored. [2]} also showed that \(^{16}\) O/\(^{18}\) O increases with increasing mass of hydrogen in the helium-burning shell. The presence of hydrogen leads to a decrease of \(^{18}\) O and increase in \(^{16}\) O due to proton capture reactions. The source of this hydrogen is a thin hydrogen envelope around the progenitor He white dwarf [1]}. The mass of the hydrogen envelope is inversely correlated with the mass of the He white dwarf [5]}, [6]}. However, a significant fraction of this hydrogen is expected to be burned during the merger. How much of the envelope hydrogen actually reaches the helium shell is not known.
